The present invention relates to a control apparatus for a direct injection engine, and particularly to a control apparatus for a direct injection engine to recover from deterioration of combustion in the compression stroke injection mode by a fuel injection valve.
For automobiles of the present time, there is a growing demand for reduction of exhaust emissions such as carbon mono oxide (CO), hydro carbons (HC), nitrogen oxides (NOx) contained in automobile emissions in view of environmental protection. One approach for reducing such emissions is a direct injection engine (in-cylinder injection type internal combustion engine). In the direct injection engine, fuel is injected through a fuel injection valve directly into the combustion chamber of a cylinder.
Fuel injection by the fuel injection valve is generally performed during intake stroke or the compression stroke of the engine. For example, when a high load and a high rotational speed are required, fuel is injected during intake stroke to effect homogeneous combustion at a stoichiometric mixture thereby stabilizing the combustion, and at the same time, when a light load and a low rotational speed are required, fuel is injected during compression stroke to effect stratified combustion at a lean mixture thereby improving the fuel consumption rate (fuel economy).
In a direct injection engine, as described above, fuel injection is performed either during intake stroke or the compression stroke depending on the operational demands. However, in the fuel injection during compression stroke, there is a problem in that combustion tends to be deteriorated due to incomplete mixing of air and fuel. To solve this problem, a direct injection engine technique having means for recovering combustion stability has been proposed (see JP-A-9-303189 for example).
The proposed technique has combustion quality recovery means, which switches the operational mode from fuel injection during compression stroke to fuel injection during intake stroke immediately after deterioration of combustion is detected during fuel injection of the compression stroke.
The above described combustion quality recovery means has a function to recover the combustion stability by changing the control parameters such air-fuel ratio, fuel injection timing, and injection timing when deterioration of combustion is detected during fuel injection of the compression stroke. Moreover, the combustion quality recovery means has also a function to perform fuel injection forcibly, so to speak, during intake stroke regardless of the detection of deterioration of combustion, thereby preventing the deterioration of combustion due to the deposits produced by the fuel injection during compression stroke when fuel injection during compression stroke has continued for a predetermined time period.
On one hand, fuel injection during compression stroke of the engine facilitate the stratification of air and fuel in the cylinder making it possible to burn the fuel concentrated around the spark plug. This will enable an operation at lean air-fuel ratio as the whole combustion chamber, and therefore would be advantageous in improving the fuel economy.
However, in the above described prior art, since the operation mode is immediately switched to fuel injection during intake stroke by terminating the fuel injection during compression stroke when deterioration of combustion is detected during fuel injection of the compression stroke, or fuel injection of the intake stroke is forcibly performed when fuel injection during compression stroke has continued longer than a preset time, there will be few drawbacks in view of combustion stability, but inconveniences would result in view of fuel consumption rate. Moreover, since switching to fuel injection during intake stroke as described above will cause a torque step at the moment of the switching, a problem arises in that the driver of the vehicle will perceive an unintended torque change as an uncomfortable feel or as a degraded drive feel.
Moreover, although the above described combustion quality recovery means according to the prior art discloses the points of switching to fuel injection during intake stroke and of changing the control parameters during fuel injection of the compression stroke, these points are described separately and independently, and there is no disclosure on the selection of these points and the priority in selecting either of them. In this prior art, there will be a problem, for example, of the buildup of deposits produced around the injection opening of the fuel injection valve. The deposits in early stages when the spray pattern of fuel starts changing can be removed by burning the deposits by fuel injection during intake stroke. However, when the amount of the deposits increases in later stages, they may not be thoroughly removed. It is considered that this phenomena will frequently occur as a factor of deterioration of combustion, and that when switching to fuel injection is performed during intake stroke, or control parameters are changed in fuel injection during compression stroke independently without a proper selection, the above described stage of deposit buildup will not be taken into account, and therefore deterioration of combustion due to the buildup of deposits will not be properly addressed.
Moreover, in the above described prior art, no consideration is given to the point that combustion stability may be enhanced by improving the mixing method of air and fuel which will affect the combustion stability.
In a direct injection engine in which fuel injection is performed during intake stroke or the compression stroke of the engine, when the spray pattern of the fuel injection valve changes due to aged deterioration, that will give an impact on the combustion stability in the case of fuel injection during compression stroke. Therefore, one approach to this problem would be switching to fuel injection during intake stroke to recover the combustion stability thereby preventing deterioration of combustion. However, such switching of fuel injection will cause a torque step giving a shock to the driver thus degrading the driving feel.
The present invention has been achieved in view of the above described problems, and its object is to provide a control apparatus for a direct injection engine, wherein deterioration of combustion due to fuel injection during compression stroke of the engine will be prevented thereby enhancing the driving feel, and fuel consumption rate will be improved by expanding the driving range by fuel injection during compression stroke.
To attain the above described object, the present invention provides a control apparatus for a direct injection engine, in which a fuel injection valve for injecting fuel directly into the cylinder is provided, and fuel injection by the fuel injection valve is performed at least during intake stroke or during compression stroke of the engine, characterized in that the control apparatus comprises combustion stabilizing means for stabilizing combustion in the cylinder, and the combustion stabilizing means comprises next operation mode determination means for enabling the selection of the operation mode for recovering combustion stability either by fuel injection during intake stroke or by fuel injection during compression stoke when a deteriorated state of combustion is detected during fuel injection of the compression stroke.
In the control apparatus for a direct injection engine configured as describe above according to the present invention, the next operation mode determination means of the combustion stabilizing means includes an operation mode for recovering combustion stability by fuel injection during intake stroke, and an operating mode for recovering combustion stability by fuel injection during compression stroke, and when a deteriorated state of combustion is detected during fuel injection of the compression stroke, either of the operation mode by the intake stroke injection or by the compression stroke injection is selected, and therefore it is possible to decrease the operation mode by the intake stroke injection and expand the operation range by fuel injection during compression stroke further than the conventional approaches. And, owing to the above described configuration, switching to fuel injection during intake stroke can be performed in response to various demands such as acceleration demand and deceleration demand from the driver or an automatic car-to-car distance control system, thus making it possible to address both problems: combustion deterioration due to deposits and degradation of driving feel due to a torque shock.
The combustion stabilizing means comprises intake stroke injection continuation means for continuing fuel injection during intake stroke for a predetermined time period when recovering the combustion stability by fuel injection during intake stroke. Alternately, the above described combustion stabilizing means comprises control parameter change means for changing the control parameters relating to the combustion when recovering combustion stability by fuel injection during compression stroke. The control parameters comprises at least one of a fuel pressure, an amount of emission gas recirculation, an opening degree of an airflow generation valve, an amount of valve-overlap of the intake and exhaust valves, and the number of fuel injection.
The next operation mode determination means selects the operation mode for recovering combustion stability by fuel injection during intake stroke in response to the number of detection of deteriorated combustion state during fuel injection of the compression stroke or the operational demands of the engine.
Alternatively, the next operation mode determination means inhibits the switching to the operation mode for recovering combustion stability by fuel injection during compression stroke when recovering combustion stability by fuel injection during intake stroke, and selects the operation mode for recovering combustion stability by fuel injection during compression stroke when continuation of the operation mode of recovering combustion stability by fuel injection during intake stroke has been performed a predetermined number of times.
The combustion stabilizing means comprises control parameter changing means for changing the control parameters relating to combustion when recovering combustion stability by fuel injection during compression stroke, and the control parameter includes at least one of fuel injection timing of the fuel injection valve, an amount of target injection, and the ignition timing.
The control parameters of fuel injection timing and the ignition timing are alternately changed.
The control parameters of fuel injection timing and the ignition timing are changed by either being advanced of retarded so that the fuel injection timing and the ignition timing respectively provide substantially equal amounts of crankshaft angle change with respect to a reference crankshaft angle at which the fuel injection timing and the ignition timing are on the same crank angle.
The combustion stabilizing means also comprises control parameter resetting means, which when a deteriorated state of combustion during fuel injection of the compression stroke is improved, resets the control parameters to the values at the time of the improvement, and stores the reset values until next deteriorated state of combustion during fuel injection on the following compression stroke is detected.
The combustion stabilizing means comprises rotational fluctuation determination means for determining the combustion state on the basis of the fluctuation of rotation of the engine.
The control apparatus has the operational region of fuel injection during compression stroke as a control map of the rotational speed and the load of the engine, or as a control map based on the rotational speed of the engine and the water temperature, and when fluctuation of rotation of the engine exceeds a predetermined threshold, the combustion stabilizing means changes those sections of the control map having exceeded the threshold from the operational region of fuel injection during compression stroke to the operational region of fuel injection during intake stroke.
The engine is equipped with a supercharger and the combustion stabilizing means limits supercharge pressure of the supercharger below a predetermined value or lower the supercharge pressure of the supercharger when the fluctuation of rotation of the engine exceeds a predetermined threshold.
The engine comprises a inner EGR mechanism for introducing the combustion gas into the cylinder by increasing or decreasing an amount of valve overlap of the intake/exhaust valves, and an outer EGR mechanism for introducing combusted gas into an intake port from other pipe path, and the combustion stabilizing means reduces an amount of the outer EGR and/or increases an amount of the inner EGR when the fluctuation of rotation of the engine exceeds a predetermined threshold.
With the engine being combined with an automatic transmission, the combustion stabilizing means comprises transmission cooperative control means which disengages lock-up of the automatic transmission when the fluctuation of rotation of the engine exceeds a predetermined threshold, and reactivate the lock-up when the fluctuation of rotation of the engine becomes lower than the predetermined threshold in a substantially same range of the rotational speed at the time of disengagement of the lock-up after the disengagement of the lock-up.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.